Polyurethane foams having an impervious outer skin and a cellular core are known and are generally obtained by foaming in a closed mold. Such polyurethane foams are eminently suitable for the mass production of light weight structures, such as for example, in the furniture, motor vehicle, and housing industries.
These polyurethane moldings are generally produced by introducing a foamable reaction mixture comprising a polyisocyanate, a compound containing at least two hydrogen atoms reactive with isocyanates and additives, into a closed heatable mold in which the foam expands and solidifies under high compression. The foamed material fills the mold and exactly reproduces the inner surface thereof.
It is generally preferred to use molds made of a material of extremely high thermal capacity and equally high thermoconductivity such as metal. It is also possible however to use molds made of other materials such as various plastics, glass or wood.
In order to prevent the foamed molding from adhering to the surface of the mold during mold release, the mold surface is generally provided with a release agent. Waxes, soaps and various silicones are commonly used as mold release agents for polyurethane systems. These mold release agents apparently form a thin film between the surface of the mold and the foamed molding, which theoretically should not adhere to either the mold or the molding and thus should enable the molding to be readily removed from the mold. Unfortunately, these types of release agents possess several disadvantages including the formation of residues of release agent on the mold surface and the formation of a thin coating of release agent on the surface of the molded product to which conventional lacquer systems do not adhere. Finally, to date, the external release agents used do not generally prevent a certain amount of delamination of the integral skin from the foam core upon removal from the mold.
In an effort to overcome these problems, the art has developed the use of talc powder as an external release agent. As discussed in U.S. patent application Serial Number 690,447, filed May 27, 1976, talc powder may be applied to a mold surface by merely dusting the powder onto the mold surface. Although talc powder has demonstrated satisfactory release properties, its application to a mold surface is cumbersome. The application of the talc powder by dusting is not only inconvenient and wasteful, it results in nonuniform deposition over the mold surface, creates a health hazard and precludes the use of liquid additives.
Thus, the search for release agents which will allow for the easy production of foams to meet substantially any property specification and which will overcome the common delamination problems and yet apply readily to a mold surface continues.